Nick didn't intend on taking prisoners to torture so the room was repurposed to house the forge since the things the forge made might be rather volatile at first. Atronachs were magical constructs and as a result wouldn't try and keep their surroundings intact when they were first "born". Nick would need to command the newly created things to restrain themselves before he allowed them out of this room. That was for later though as at this moment Nick started to take the individual rings of the forge out of the realm and setting them in place at the center of the room.-
At first glance the now set up forge looked like several large rings laid within each other by size covered in dense jagged looking runes. But when Nick tapped his wand on the largest ring that was at the outermost part of the set up and dumped his entire mana reserve into it this changed. All of the rings began to hum and float into the air while the runes glowed an brilliant blue. Nick noticed that the amount of mana he used was only barely enough to activate the forge but nowhere near enough to use it.-
This didn't bother him as he had already predicted that this would happen using context clues about the world from which the forge originated. Nirn was a world that was positively drenched in mana to the point magical creatures had been recorded manifesting from thin air , such as was the case with the ice wraiths. Obviously the enchantments and magic of such a place would likely not work with extreme efficiency in mind like this worlds magical processes did. Nick had already taken that into mind when he was tweaking the original schematics rune lay out for the forge.-
His version was much more efficient than the original but even then it was an absolute mana drain of heavy proportions to use the forge. Thankfully he had taken this into account and had Dotty and Lucas placing daedric runestones at the edge of the island for the past month. Each rune stone served as a sort of mana collector and focus that will draw in the mana and confine it to the island raising the mana density massively. The final step of his plan however was to place the keystone of this array of runestones in the center of the manor so that most of the loose mana concentrates there.-
At the moment the runes stones weren't active but he didn't doubt at all that once he started to activate them it would create a huge commotion. After all all the mana detecting instruments in the world would likely register the massive flow of energy directed at at single location. It would of course stabilize in a short period of time but Nick still needed to worry about people figuring out where the island was before it did so.-
He had taken this into account as well and added a delayed activation function of varying times to each of the runestones. This meant that even though they would all activate the moment the keystone did it would take a awhile before each stone began to draw in mana. This delay was just long enough that it would trick all but the most sensitive instruments into not noticing it. For people like Luna that could sense mana in some manner though they would notice it flowing in a different direction and probably ignore it. So when Nick activated the keystone in the center of the manor he was relaxed.-
He had wanted to use his realm for the forge originally but he had a spark of enlightenment and realized that he was actually MORE likely to have it discovered there and settled for the island instead. It would take about a month in total for the runestones to all work fully and saturate the island in mana. In theory this should act as a simulation of what the entire world will experience after Grindelwald is done. Nick expected the island to undergo either evolution or atavism as the plants and animals on it adapt to the mana or revert back to their more powerful ancestral forms.-
Nick was almost regretful that he didn't have a dragon on the island to see what the atavist form of the creature was. Still once he had the mana he needed to use the forge Nick knew he was going to start creating an army of atronachs for the future. This led him to his next course of action that was rather irritating to deal with , bloodbinding gems to himself. To ensure that the atronachs were "born" unswayably loyal to him Nick needed to soak the gems he used as their base component while making them in his blood.